The present invention relates to a downhole tool for, and a method of, generating a drive force in a downhole environment. In particular, but not exclusively, the present invention relates to downhole tools for generating rotary and axial drive forces in a downhole environment.
Tools for generating a drive force in a downhole environment are known in the oil/gas industry. These include downhole motors, turbines and setting tools. Turbines are fluid driven and are run on a string of tubing, with associated fluid circulation apparatus at surface. Whilst this is an effective procedure for most drilling applications, it is time-consuming and expensive for secondary drilling applications, such as removing an obstruction in a borehole or de-scaling and hydrate removal procedures.
Setting tools are used to generate a force to set tools such as plugs, packers and the like, which are initiated by a tensile/compressive load. One known setting tool is the pyrotechnic setting tool which generates high forces by ignition/detonation of a pyrotechnic charge. The pyrotechnic charge is housed in a pressure-tight piston chamber, and detonation generates a controlled burn, releasing gases which generate significant pressure in the chamber. This pressure acts on a piston which “strokes”, generating a high force, similar to a hydraulic ram, and this force is applied directly to the tool to be set. There are many disadvantages associated with pyrotechnic tools. For example, pyrotechnic charges are require delicate handling under very stringent regulations. Export/import of explosives into and out of certain regions of the world is prohibited. Use of the tool involves significant risks to personnel and structures. An electrical charge is required to ignite or detonate the charge and this limits use of the tool mainly to electric wireline applications. In such applications, radio silence must be enforced in the vicinity of the setting tool during deployment. If the setting tool is deployed on slick wireline, a battery operated trigger or detonator is required which operates on a timer basis, limiting its uses. Finally, failure of the charge to properly detonate creates a significant handling problem.